Triaxial accelerometer zero offset calibration method, computing device, and storage medium

Abstract

This invention provides a zero-bias calibration method, computing device, and storage medium for a triaxial accelerometer. The zero-bias calibration method includes: placing the triaxial accelerometer sequentially in at least three different postures within a plane defined by the Z and Y axes for a predetermined duration, to obtain a set of acceleration measurements output by the triaxial accelerometer in each posture, each set of acceleration measurements including acceleration measurements along the three axes; and calculating the zero bias b of the Y and Z axes based on the obtained at least three sets of acceleration measurements and a predetermined formula. y ,b z The predetermined formula is constructed based on the modulus of the true triaxial acceleration as the local gravitational acceleration. This allows for zero-bias calibration with only at least three measurements in different orientations, and eliminates the need for a high-precision turntable or horizontal marble platform.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of accelerometer, in particular to a three-axis accelerometer zero offset calibration method, a computing device and a storage medium. BACKGROUND

[0002] Currently, the zero offset calibration of three-axis accelerometer is usually implemented by using six position method. The calibration needs to use high-precision turntable or horizontal marble platform to rotate the accelerometer to at least six different postures, i.e. six positions in which the ±X, ±Y and ±Z axes of the accelerometer are perpendicular to the horizontal plane.

[0003] With the increase of the use time of MEMS (Micro-Electro-Mechanical System) accelerometer, the zero offset of the accelerometer will change to different degrees, resulting in the performance degradation of the accelerometer. At this time, the accelerometer is usually installed on the customer equipment, and the cost of disassembling and returning the accelerometer to the factory for re-calibration is high. The customer needs to use the above-mentioned six position method for self-calibration, which needs professional equipment such as turntable or horizontal marble platform, and may need to disassemble and install the accelerometer, which is time-consuming and laborious.

[0004] Therefore, it is necessary to propose an improved scheme to overcome the related problems. SUMMARY

[0005] The present application relates to the field of accelerometer, in particular to a three-axis accelerometer zero offset calibration method, a computing device and a storage medium.

[0006] To achieve the purpose of the application, according to one aspect of the present application, the present application provides a three-axis accelerometer zero offset calibration method, which comprises: sequentially placing the three-axis accelerometer in at least three different postures in the plane defined by the Z axis and the Y axis for a predetermined time, to obtain a group of acceleration measurement values of the three-axis accelerometer output at each posture, each group of acceleration measurement values including acceleration measurement values of three axes; solving the zero offsets b y ,b z of the Y axis and the Z axis according to the obtained at least three groups of acceleration measurement values and a predetermined formula.

[0007] In one embodiment, the predetermined formula is:

[0008]

[0009] Substituting the obtained at least three groups of acceleration measurement values into the predetermined formula to solve the zero offsets b y ,b zwherein x i i are acceleration measurements of Y-axis and Z-axis of the triaxial accelerometer respectively, r is the local gravity acceleration, and i is the serial number of at least three different postures.

[0010] According to one aspect of the present application, the present application provides a method for calibrating zero offset of a triaxial accelerometer, which comprises: placing the triaxial accelerometer in four different postures defined by X-axis, Y-axis and Z-axis in a three-dimensional space for a predetermined time duration in sequence, so as to obtain a set of acceleration measurements output by the triaxial accelerometer in each posture, each set of acceleration measurements comprising acceleration measurements of three axes; and solving zero offsets b x y z of X-axis, Y-axis and Z-axis based on the four sets of obtained acceleration measurements and a predetermined formula, wherein the predetermined formula is constructed according to a modulus of true values of triaxial accelerations being the local gravity acceleration.

[0011] In one embodiment, the predetermined formula is:

[0012]

[0013] The four sets of obtained acceleration measurements are substituted into the predetermined formula to solve the zero offsets b x y z of X-axis, Y-axis and Z-axis, wherein x i i i are acceleration measurements of X-axis, Y-axis and Z-axis of the triaxial accelerometer respectively, r is the local gravity acceleration, and i is the serial number of at least three different postures.

[0014] According to another aspect of the present application, the present application provides a computing device comprising a processor and a memory, wherein the memory stores program instructions executed by the processor to implement the above-mentioned method for calibrating zero offset of a triaxial accelerometer.

[0015] According to still another aspect of the present application, the present application provides a storage medium storing program instructions executed to implement the above-mentioned method for calibrating zero offset of a triaxial accelerometer.

[0016] Compared with the prior art, the present application solves the zero offsets of three or two axes based on the predetermined formula constructed according to a modulus of true values of triaxial accelerations being the local gravity acceleration by ignoring the accelerometer scale factor error, so that the present application only needs measurements of at least three different postures and does not need a high-precision turntable or a horizontal marble platform to complete the zero offset calibration. BRIEF DESCRIPTION OF DRAWINGS ​​​​​​​

[0017] Figure 1 Flow chart of a zero offset calibration method for a tri-axial accelerometer in a first embodiment of the present application;

[0018] Figure 2 Flow chart of a zero offset calibration method for a tri-axial accelerometer in a second embodiment of the present application;

[0019] Figure 3 Schematic diagram of four poses of an excavator equipped with a tri-axial accelerometer in the present application;

[0020] Figure 4 Schematic diagram of an excavator tilted and with an installation error of the accelerometer in the present application;

[0021] Figure 5 Schematic diagram of the distribution of readings of a tri-axial accelerometer in four poses in three different views. DETAILED DESCRIPTION

[0022] In order to further clarify the technical means and effects adopted by the present application to achieve the predetermined inventive objectives, the specific embodiments, structures, features and effects thereof according to the present application are described in detail below in combination with the drawings and preferred embodiments.

[0023] The present solution proposes a new zero offset calibration method for a tri-axial accelerometer, which only needs to control the tri-axial accelerometer to rotate to at least 3 or 4 different poses to achieve the zero offset calibration of 2 or 3 axes of the accelerometer, without the need for high-precision turntables or horizontal marble platforms and other equipment, and without the need to rotate the accelerometer to a specific 6 different poses for calibration.

[0024] Figure 1 Flow chart of a zero offset calibration method 100 for a tri-axial accelerometer in a first embodiment of the present application. In the first embodiment, the zero offset calibration method 100 can achieve the zero offset calibration of two axes of the tri-axial accelerometer. The following takes an example of a tri-axial accelerometer installed on an excavator 210 to illustrate the zero offset calibration method in the present application. However, it is obvious that the tri-axial accelerometer can also be installed on other vehicles or equipment, and the zero offset calibration method in the present application can also be used in these applications.

[0025] As shown in the flow chart, the zero offset calibration method 100 includes the following steps. Figure 1

[0026] Step 110, sequentially place the tri-axial accelerometer in at least three different poses in the plane defined by the Z axis and the Y axis for a predetermined time length, to obtain a set of acceleration measurement values of the tri-axial accelerometer output in each pose, each set of acceleration measurement values including acceleration measurement values of three axes. ​

[0027] Specifically, the accelerometer is mounted on a boom, an arm, a stick or a bucket of the excavator, and the excavator controls the boom, the arm, the stick or the bucket so that the accelerometer is sequentially placed in at least three different postures in a plane defined by the Z axis and the Y axis, such as Figure 3 As shown, four different postures are shown here, and the four different postures are P1, P2, P3 and P4 respectively. The predetermined time length can be greater than 3 seconds, such as 4, 5, 7 seconds, etc. The average acceleration of each axis of the three-axis accelerometer during the static period is taken as the acceleration measurement value of the axis, which can eliminate part of the measurement error. In the four postures, the X axis always remains approximately horizontal, i.e. parallel to the ground, so the difference in the acceleration measurement value of the X axis in each group of acceleration measurement values is small, such as less than a predetermined threshold. In the first embodiment, the zero offset of the X axis cannot be calibrated, and only the zero offsets of the Z axis and the Y axis can be calibrated. Of course, three groups of acceleration measurement values in three postures can also be collected for subsequent zero offset calibration. In addition, even if the X axis is not set horizontally, the X axis can be made horizontal through subsequent tilt calibration.

[0028] In one embodiment, the maximum angle difference between the angle of the Y axis and the gravity line in each posture is greater than a first predetermined angle threshold, and the maximum angle difference between the angle of the Z axis and the gravity line in each posture is greater than a second predetermined angle threshold. Specifically, as shown, Figure 3 As shown, the angle of the Y axis and the gravity line is the smallest in the P1 posture, and the angle of the Y axis and the gravity line is the largest in the P2 posture, so the angle difference between the angle of the Y axis and the gravity line in the P1 posture and the angle of the Y axis and the gravity line in the P2 posture is the maximum angle difference, which is approximately more than 180 degrees. Similarly, as shown, Figure 3 As shown, the angle of the Z axis and the gravity line is the smallest in the P1 posture, and the angle of the Z axis and the gravity line is the largest in the P4 posture, so the angle difference between the angle of the Z axis and the gravity line in the P1 posture and the angle of the Z axis and the gravity line in the P4 posture is the maximum angle difference, which is approximately more than 180 degrees. When the maximum angle difference is relatively large, the subsequent zero offset calibration effect will be more accurate. For smaller maximum angle difference, the zero offset calibration method in the present application is also applicable.

[0029] In one embodiment, the first predetermined angle threshold and the second predetermined angle threshold are both greater than or equal to 30 degrees.

[0030] It should be noted here that in the present application, the plane in which the stick 220 of the excavator can move is defined as the plane of the Y axis and the Z axis, and the direction perpendicular to the movable plane is defined as the X axis. The X axis, the Y axis and the Z axis are defined when the accelerometer is mounted. In other descriptions, other definition methods can also be used.

[0031] Specifically, such as Figure 3 As shown, the inertial measurement unit can first remain stationary at attitude P1 for 5 seconds, then move from attitude P1 to attitude P2, remain stationary at attitude P2 for 5 seconds, then move from attitude P2 to attitude P3, remain stationary at attitude P3 for 5 seconds, and then move from attitude P3 to attitude P4, remaining stationary at attitude P4 for 5 seconds. In each attitude, the accelerometer can sample and obtain acceleration measurements.

[0032] Step 120: Solve for the zero offsets by and b of the Y-axis and Z-axis based on at least three sets of acceleration measurements and predetermined formulas. z The predetermined formula is constructed based on the modulus of the true value of triaxial acceleration being the local gravitational acceleration.

[0033] In one embodiment, the predetermined formula is:

[0034]

[0035] Substitute the obtained at least three sets of acceleration measurements into the predetermined formula to solve for the zero offset b along the Y and Z axes. y ,b z , where y i ,z i These are the acceleration measurements along the Y and Z axes of the triaxial accelerometer, respectively, where r is the local gravitational acceleration and i is the sequence number of at least three different attitudes. The X-axis is typically parallel to the ground plane; even if it is not, compensation is needed to make it parallel to the ground.

[0036] The derivation process of the above-mentioned predetermined formula is described below.

[0037] The measurement model of the accelerometer is as follows:

[0038]

[0039] in: f is the accelerometer measurement value, f is the true value of the accelerometer, and b is the accelerometer reading. f s represents the zero bias of the accelerometer, and s represents the scale factor error of the accelerometer.

[0040] Based on practical engineering experience, the accelerometer scale factor error is generally small, so equation (1) can be simplified to:

[0041]

[0042] Let: x i ,y i ,z i b is the measurement value from the triaxial accelerometer. x ,b y ,bz Let r be the zero bias of each axis of the triaxial accelerometer, and r be the local gravitational acceleration. Based on the fact that the magnitude of the true value of the triaxial acceleration is the local gravitational acceleration, the equation is constructed as follows:

[0043] (x i -b x ) 2 +(y i -b y ) 2 +(z i -b z ) 2 =r 2 (3)

[0044] Equation (3) shows that the zero-bias calibration of a triaxial accelerometer is essentially a problem of solving for the center and radius of a sphere based on sphere fitting. That is, given the coordinates of multiple points (at least three in the first embodiment) on the surface of a spatial sphere, the coordinates of the center and the radius are solved. Therefore, the more dispersed the distribution of multiple points on the sphere, the more accurate the sphere fitting result will be. In special cases, when the distribution of multiple points is approximately circular, equation (3) degenerates into a planar circle equation. For example, in the calibration example of a triaxial accelerometer in an excavator, the X-axis data of multiple attitudes of the accelerometer are very different, and in this case, the equation must be solved based on circle fitting.

[0045] Expanding and rearranging equation (3), we get:

[0046]

[0047] For simplicity, formula (4) can be rearranged as follows:

[0048]

[0049] Where: A = 2b x B = 2b y C = 2b z ,

[0050] When there are 4 sets of accelerometer measurements, equation (5) can be written in matrix form:

[0051]

[0052] Equation (6) was solved using Gaussian elimination, and the unknowns A, B, C, and D were obtained. The zero bias of the 3-axis accelerometer and the local gravitational acceleration were then obtained as follows:

[0053] b x =A / 2

[0054] b y =B / 2

[0055] bz = C / 2

[0056]

[0057] In the application example in which the triaxial accelerometer is arranged on the excavator, the measured value of the X axis changes little in each attitude, so that the zero offset of the X axis cannot be obtained, and thus only the term related to the X axis in formula (4) needs to be set to 0. In this way, formula (4) can be simplified as the predetermined formula:

[0058]

[0059] At this time, only 3 sets of acceleration measurement values in 3 attitudes are needed to obtain the zero offset b y z .

[0060] In practice, taking the application of the excavator as an example, when the uneven road surface causes the body of the excavator to tilt and the accelerometer to have installation errors, as shown in FIG. 2, the numerical difference of the X axis of the triaxial accelerometer in several attitudes is obvious, which causes obvious errors when the circular fitting is used to solve the zero offset of the accelerometer. Figure 4

[0061] As shown in FIG. 3, it respectively shows the distribution diagram of the triaxial readings of the accelerometer in 4 attitudes in 3 different views (a, b and c), wherein L1 is the triaxial reading distribution of the accelerometer when the body tilt angle is 0 degree, and L2 is the triaxial reading distribution of the accelerometer when the body tilt angle is 10 degrees. Figure 5 As shown in FIG. 4, the gravity line forms an inclination angle with the plane defined by the Z axis and the Y axis, and at this time, the accelerometer is in a tilted state.

[0062] Figure 4 The zero offset calibration method 100 further comprises:

[0063] calculating the attitude angle in at least three different attitudes according to at least three sets of acceleration measurement values;

[0064] calculating the tilt attitude matrix R tilt_i in at least three different attitudes of the tilted state and the normal attitude matrix R ⊥_i in at least three different attitudes of the normal state according to the calculated attitude angle in at least three different attitudes, and further obtaining the rotation matrix R tilt_i from the tilt attitude matrix R ⊥_i to the normal attitude matrix R

[0065]

[0066] using the rotation matrix R ​​​​Compensate each set of acceleration measurements output by the tri-axial accelerometer, and substitute each set of compensated acceleration measurements into the predetermined formula to solve the Y-axis and Z-axis zero offsets b y ,b z .

[0067] wherein the attitude angles are [Yaw i , Pitch i , Roll i ], Yaw is a yaw angle, Pitch is a pitch angle, and Roll is a roll angle, and the Pitch i in the attitude angles in at least three different attitudes of the tilted state is the tilt angle, and the Pitch i in the attitude angles in at least three different attitudes of the normal state is 0, and the Yaw i are all 0.

[0068] The compensated acceleration measurements are:

[0069]

[0070] wherein are the acceleration measurements before compensation.

[0071] In this way, the two-axis zero offset calibration of the accelerometer can be completed without disassembling the accelerometer, and the operation is simple and fast.

[0072] Figure 2 is a flow chart of the tri-axial accelerometer zero offset calibration method 200 in the second embodiment. In the second embodiment, the zero offset calibration method 200 can realize the zero offset calibration of the three axes of the tri-axial accelerometer. However, in this embodiment, the tri-axial accelerometer needs to be disassembled from the installation device, such as the excavator.

[0073] As shown in Figure 2 , the zero offset calibration method 200 comprises the following steps.

[0074] Step 210, sequentially place the tri-axial accelerometer in at least four different attitudes in the three-dimensional space defined by the X-axis, Z-axis and Y-axis for a predetermined time period, so as to obtain a set of acceleration measurements output by the tri-axial accelerometer in each attitude, and each set of acceleration measurements comprises acceleration measurements of the three axes.

[0075] Specifically, the accelerometer is disassembled from the excavator, and the accelerometer is sequentially placed in at least four different attitudes in the three-dimensional space defined by the X-axis, Z-axis and Y-axis.

[0076] For example, in the first attitude, the acceleration measurement of the three-axis accelerometer along the X-axis is +1g, while the acceleration measurements of the other two axes are 0. In the second attitude, the acceleration measurement of the three-axis accelerometer along the Y-axis is +1g, while the acceleration measurements of the other two axes are 0. In the third attitude, the acceleration measurement of the three-axis accelerometer along the Z-axis is +1g, while the acceleration measurements of the other two axes are 0. In the fourth attitude, the acceleration measurement of the three-axis accelerometer along the X-axis is -1g, while the acceleration measurements of the other two axes are 0. In other examples, any other four attitudes can be set, as long as at least one attitude is not coplanar with the other three attitudes, i.e., the four attitudes are not in the same plane.

[0077] Furthermore, as mentioned above, equation (3) indicates that the zero-bias calibration of a triaxial accelerometer is essentially a problem of solving for the center and radius of a sphere based on sphere fitting. That is, given the coordinates of at least four points on the surface of the sphere (i.e., four sets of acceleration measurements corresponding to four attitudes), the coordinates of the center and the radius are solved. Therefore, the more measurements there are and the more dispersed the distribution of measurement points on the sphere, the more accurate the sphere fitting result will be.

[0078] Step 220: Based on the obtained at least four sets of acceleration measurements and predetermined formulas, solve for the zero offset b of the X-axis, Y-axis, and Z-axis. x ,b y ,b z The predetermined formula is constructed based on the modulus of the true value of triaxial acceleration being the local gravitational acceleration.

[0079] Specifically, the predetermined formula is:

[0080]

[0081] Substitute the obtained at least four sets of acceleration measurements into the predetermined formula to solve for the zero bias b of the X-axis, Y-axis, and Z-axis. x ,b y ,b z , where x i ,y i ,z i These are the acceleration measurements of the X, Y, and Z axes of the triaxial accelerometer, respectively, where r is the local gravitational acceleration and i is the sequence number of at least three different attitudes. The predetermined formula is formula (3) in the first embodiment. The derivation and solution principle of formula (3) will not be repeated here.

[0082] In one embodiment, the maximum angle difference between the Y-axis and the gravity line in the four different postures is greater than a first predetermined angle threshold, the maximum angle difference between the Z-axis and the gravity line in the four different postures is greater than a second predetermined angle threshold, and the maximum angle difference between the X-axis and the gravity line in the four different postures is greater than a third predetermined angle threshold.

[0083] Specifically, the first, second and third predetermined angle thresholds are greater than or equal to 30 degrees.

[0084] The zero offset calibration method of the application does not depend on a high-precision turntable or a horizontal marble platform, and can be completed on a common platform, such as a desktop.

[0085] According to another aspect of the application, the application provides a computing device comprising a processor and a memory, the memory storing program instructions executed by the processor to implement the above-mentioned zero offset calibration method of the three-axis accelerometer.

[0086] According to still another aspect of the application, the application provides a storage medium storing program instructions executed to implement the above-mentioned zero offset calibration method of the three-axis accelerometer.

[0087] In this document, the terms "comprise", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, in addition to containing the listed elements, other elements not explicitly listed can also be contained.

[0088] In this document, the terms "comprise", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, in addition to containing the listed elements, other elements not explicitly listed can also be contained.

[0089] In the case of no conflict, the above-mentioned embodiments and features in the embodiments can be combined with each other.

[0090] The above-mentioned only the preferred embodiments of the application, and not to limit the application, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application, should be included in the protection scope of the application.

Claims

1. A method of zero offset calibration of a tri-axial accelerometer, characterized by, It comprises: placing the tri-axial accelerometer in at least three different postures in the plane defined by the Z-axis and Y-axis for a predetermined time period in each posture to obtain a set of acceleration measurements of the tri-axial accelerometer output in each posture, each set of acceleration measurements comprising acceleration measurements of the three axes; b y, b z , the predetermined formula is constructed according to a module of the true value of the three-axis acceleration being the local gravitational acceleration, the accelerometer is mounted on a boom, arm, stick or bucket of an excavator, and the excavator is controlled to place the accelerometer in at least three different postures in the plane defined by the Z-axis and Y-axis, the predetermined formula is: The at least three sets of acceleration measurements are substituted into the predetermined formula to solve for the zero offset b of the Y and Z axes y z where y i and z i are the acceleration measurements of the Y and Z axes, respectively, of the three-axis accelerometer, and r is the index number of the at least three different orientations.​ 2. The zero offset calibration method of claim 1, wherein, the difference between the acceleration measurements of the X-axis in each set of acceleration measurements is less than a predetermined threshold, the maximum angle difference between the Y-axis and the gravity line in the at least three different postures is greater than a first predetermined angle threshold, and the maximum angle difference between the Z-axis and the gravity line in the at least three different postures is greater than a second predetermined angle threshold.

3. The zero offset calibration method of claim 2, wherein, the first predetermined angle threshold is greater than or equal to 30 degrees, the second predetermined angle threshold is greater than or equal to 30 degrees, and the X-axis is parallel to the ground.

4. The zero offset calibration method of claim 1, wherein, the gravity line forms an inclination angle with the plane defined by the Z-axis and Y-axis when the accelerometer is in a tilted state, It further comprises: calculating the posture angle in the at least three different postures according to the at least three sets of acceleration measurements; calculating a tilt attitude matrix R of the at least three different attitudes of the tilt state according to the calculated attitude angles of the at least three different attitudes tilt_i and a normal attitude matrix R of the at least three different attitudes of the normal state ⊥_i , and further obtaining a rotation matrix R from the tilt attitude matrix R tilt_i to the normal attitude matrix R ⊥_i Compensating each set of acceleration measurements output by the three-axis accelerometer using the rotation matrix R , and substituting each set of compensated acceleration measurements into the predetermined formula to solve for the zero offsets b y , z of the Y and Z axes.​ 5. The zero offset calibration method of claim 4, wherein the attitude angles are [Yaw i , Pitch i , Roll i ], Yaw is the yaw angle, Pitch is the pitch angle, Roll is the roll angle, Pitch i is the tilt angle among the attitude angles in at least three different attitudes of the tilt state, Pitch i is 0 among the attitude angles in at least three different attitudes of the normal state, Yaw i are all 0, Compensated acceleration measurement is: wherein is the acceleration measurement before compensation.

6. The zero offset calibration method of claim 1, wherein the predetermined time period is greater than 3 seconds, and the average acceleration of each axis of the accelerometer in the rest period is taken as the acceleration measurement of each axis.

7. A computing device comprising a processor and a memory, the memory having stored therein program instructions that, when executed by the processor, implement the zero offset calibration method of the tri-axial accelerometer according to any one of claims 1-6.

8. A storage medium having stored therein program instructions that, when executed, implement the zero offset calibration method of the tri-axial accelerometer according to any one of claims 1-6.

Images